Why are the subfamily relationships of Triatominae (Hemiptera: Reduviidae) important?-This question is really two: Is Triatominae a phylogenetically valid monophyletic subfamily; and, if it is, to what other reduviid subfamilies is it most closely related? If the answer to the first question is Yes, then what one knows about one member of Triatominae may be true for other members; if the answer is No, then no such prediction can be made. Because many members of Triatominae are of medical importance, such predictions are vitally (literally) important. For the same reason, knowledge of the subfamily relatives of medically important triatomines is important: For here too predictions about one related member can be based on knowledge of others. These points are discussed here, and the evidence for and against (especially against) monophyly of Triatominae is also discussed. The status of Linshcosteus, the only Old World genus of Triatominae, is also discussed.